1) Field of the Invention
The present invention relates to a transmission having a transmissive member fixedly fitted with a rotary shaft, an image formation apparatus including the transmission, and a transmission manufacturing method.
2) Description of the Related Art
Transmissions are employed widely in various machines. For example, a transmission is used in image formation apparatuses to rotate a transmissive member. The rotational force is transmitted, via a rotary shaft, to a photosensitive drum that carries a toner image. The transmissive member includes gears and pulleys. Such a technology has been disclosed in, for example, Japanese Patent Application Laid-open Publication No. H7-239596 on pages 7 and 8, and in FIG. 6.
However, if the transmissive member makes an angle with the rotary shaft, there occurs variation in the speed of the rotations transmitted. This problem will be explained in detail taking the above-mentioned publication as an example. This publication discloses to fit the photosensitive drum to the rotary shaft, fit the transmissive member to the rotary shaft, and drive the rotary member by a motor. The transmissive member includes gears and shafts. The rotation axes of the gears are perpendicular to the rotary shaft. However, if the rotation axes of the gears are not perfectly perpendicular to the rotary shaft, even if the gears are rotated at constant speed, the rotations are not properly conveyed to the rotary shaft, and hence the photosensitive drum does not rotate at desired speed. As a result, a desired toner image can not be formed on the photosensitive drum and the image quality degrades.
One approach to solve the above mentioned problem is to provide a member (hereafter, “regulative member”) that regulates the angle of the gears of the transmissive member. This regulative member is, for example, fixed to the rotary shaft and pressed against the gears of the transmissive member in such a manner that the rotation axes of the gears are perfectly perpendicular to the rotary shaft. The regulative member is fit to the rotary shaft with a screw. However, when the screw is fastened, the fastening force imposes a large stress on the regulative member and deforms the regulative member. This deteriorates the state of perfect perpendicularity of the rotation axes of the gears with the rotary shaft.